Hydraulic cylinder with pressure control

ABSTRACT

A pressure-actuated control valve which is responsive to an increase in pressure in the contracting or discharge chamber of a hydraulic actuator to restrict discharge flow from said chamber thereby reducing the velocity of the movable barrier therein. The operation of the valve is conditional on inlet pressure as it is held in a nonrestricting position by pressure fluid being admitted to the intake or expanding chamber and moves to a flowrestricting position only when a predetermined loss of pressure occurs in the intake chamber. An additional valve may be included in the system which places the actuator discharge and intake supply passages in communication to shunt fluid therebetween when discharge chamber pressure increases to a predetermined value.

United States Patent [72] Inventor John F. Phillips Hutchinson, Kans. [21] Appl. No. 819,655 {22] Filed Apr. 28, 1969 [45] Patented Oct. 19, 1971 [73] Assignee The Cessna Aircraft Company Wichita, Kans.

[54] HYDRAULIC CYLINDER WITH PRESSURE CONTROL I 10 Claims, 5 Drawing Figs.

[52] U.S. Cl.; 91/26, 91/396, 91/413, 91/420, 91/421 [51] Int. Cl ..Fl5b 15/22, F1 5b 13/07 [50] Field of Search 91/420, 394, 396, 421 25, 26, 413

[5 6] References Cited UNITED STATES PATENTS 3,523,490 8/1970 Bianchetta 91/420 Primary Examiner-Martin P. Schwadron Assistant Examiner-Allen M. Ostrager Attorneys--Gregory J. Nelson and Miller & Brown ABSTRACT: A pressure-actuated control valve which is responsive to an increase in pressure in the contracting or discharge chamber of a hydraulic actuator to restrict discharge flow from said chamber thereby reducing the velocity of the movable barrier therein. The operation of the valve is conditional on inlet pressure as it is held in a nonrestricting position by pressure fluid being admitted to the intake or expanding chamber and moves to a flow-restricting position only when a predetermined loss of pressure occurs in the intake chamber. An additional valve may be included in the system which places the actuator discharge and intake supply passages in communication to shunt fluid therebetween when discharge chamber pressure increases to a predeter' mined value.

PAIENTEDUCT 1s nan 3 6 13 ,5 o 3 j sum 18F 4 "III/A? 2 I MW I if INVENTOR. JOHN F. PHILLIPS FIG. I 1%??1 PATENTEDUBI 19 191' 3,613,503

SHEET 2 OF 4 llo INVENTOR.

JOHN F. PHILLIPS PAIENTEDUEHQIQH 3.513.503

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I VIZNTOR.

T TORNEY HYDRAULIC CYLINDER Wl'lll PRESSURE CONTROL This invention relates to hydraulically actuated motors of the linear or' rotary cylinder type. More particularly, this invention relates to a pressure-actuated valving system, for use with both single or tandem cylinder systems, for controlling the velocity at which the piston may travel during reciprocation, the velocity regulation being conditional upon inlet pressure. Further, my invention provides, in several embodiments, a valve actuated by discharge chamber pressure for shunting fluid between the inlet and discharge passages to assist in velocity control and cushioning.

Economy and efficiency of operation demands that hydraulically operated mechanisms such as booms, backhoes, and the like, perform their work functions at maximum velocity. However, excessive velocity of the movable piston or vane can be harmful causing a loss of working pressure and cavitation in the expanding chamber. Further, in high-speed operation at the end of the stroke, the piston or vane must be brought to a controlled stop. inertia loads add kinetic energy in the system which must be absorbed in a way to prevent shock loads and sudden pressure buildups that can damage the cylinder and hydraulic system.

Several schemes for governing cylinder piston velocity can be found in the prior art. For example, it is known to provide a biased floating-spool-type velocity-limiting member positioned in the cylinder inlet-outlet passage. The floating spool is movable to vary the permitted volume flow of fluid outward through the inlet-outlet passage in response to a pressure differential arising due to flow velocity out of the contracting cylinder chamber or in response to a predetermined rise in discharge chamber pressure.

One disadvantage of a simple pressure-controlled flow restrictor is that it serves to limit the velocity of the piston even if no pressure drop occurs in the expanding cylinder chamber. Although the fluid-supply pump of the'system is keeping up with the load and is ableto meet the volume requirements of the cylinder, the control may act to restrict piston travel. Asmentioned above, it is desirable to achieve 1 maximum piston velocity limited only by the ability of the system to maintain an adcquatesupply of pressure fluid to the cylinder. I

It is, therefore, a broad object of the present invention to provide a velocity control for hydraulic actuators which serves to restrict discharge flow and which is operatively conditional upon the fluid inlet pressure to the actuator.

Another broad object of this invention is to provide a linear tandem cylinder system which is provided with means for governing the velocity of piston travel within the cylinders. 1

Another object of this invention is to provide an improved means of cushioning deceleration in a hydraulic actuator as the movable barrier approaches the extreme end of its travel.

A more specific object is the provision ofan improved progressively restricting metering member which acts to restrict the outward volume of flow from the contracting cylinder chamber to provide a cushioned piston deceleration.

These and other objects of the present invention will become clear when taken in conjunction with the specification and drawings in which: I

FIG. 1 is a partial cross-sectional view of a linear cylinder provided with piston velocity control means and its associated hydraulic circuit;

FIG. 2 shows, partially in pictorial and partially schematic, a double-acting cylinder including the velocity control system;

FIG. 3 is a combined pictorial and schematic of a tandem hydraulic cylinder system, each cylinder being provided with the automatic piston velocity control valve and a second shunt valve to assist in velocity control and cushioning;

FIG. 4 illustrates a cylinder having a piston equipped with an alternate embodiment of means for progressively restricting discharge flow; and

FIG. 5 is an enlarged broken-out view of the velocity control spool shown in FIG. 3

Generally, according to the present invention, a floating restricting valve member is provided in the actuator in a passage transverse to and intersecting the cylinderinlet-outlet passage which when actuated retards discharge flow through the inlet-outlet passage. One end of thefloating restrictor is subject to the pressure existing in the contracting cylinder chamber. The floating valve is biased in a fully nonrestricting position by inlet or supply pressure fluid being admitted to the expanding piston chamber. When inlet or supply pressure drops below a certain predetermined value and expanding chamber pressure increases to a predetermined value, the float member is responsive to the differential pressure acting at its ends to move into the inlet-outlet passage to restrict outlet flow from the cylinder, causing a pressure increase in the contracting cylinder chamber which acts to retard the movement of the piston. The floating spool flow restrictor of the present invention'is particularly adaptable for use with a tandem cylinder system.

An additional feature of my invention includes a flowrestricting or metering member which is movable with the piston of a linear cylinder to progressively restrict flow from the cylinder as the piston nears the end of the stroke providing a gradual, cushioned stop. Also a shunt valve may be included which, when actuated by pressure in the discharge chamber, places the inlet and discharge passages in communication to assist in the velocity control and cushioning phases.

Turning now to the drawings in which the same numerals throughout the views identify similar elements, FIG. 1 shows a hydraulic circuit generally indicated as 10, including linear cylinder 11 having a movable piston 12 and rod 13 connected to an external work load, not shown.

Cylinder 11 is divided by piston 12 into chambers 14 and 15. Hydraulic motive fluid is supplied by pump [6 through lines 17 and 18. Valve 19 controls the direction of movement of piston 12 by admitting fluid through either line 17 or 18 to the cylinder. For example, if valve 19 is moved to the right,

fluidfrom pump 16 enters chamber 14 through line 17 causing inward travel of piston 12 and retraction of rod 13. Fluid is exhausted to reservoir 20 from chamber 15 through line l8. Relief valve 21 protects the system for overpressurization bypassing fluid, when necessary, to reservoir 20.

The novel velocity control feature is contained within end wall 25 of cylinder ll. Within the end wall is transverse passage 26 which is intersected by a passage designated as 27. Passage 27 connects fluid conduit 18 with chamber 15 and is made up of upper duct 28 and lower duct 29 which communicate through a portion of transverse passage 26 designated as 30. It will be seen that section 30 acts as an orifice to restrict flow through the passage and cause a corresponding drop in the fluid pressure through the passage. Fluid line 17 is in communication with cylinder chamber 14 through transfer duct 32 and passage 33 which is located in end wall 25 and is in communication with the left end of transverse passage 26.

Another short duct 34 also intersects passage 26 and places the right end of this passage in communication with cylinder chamber 15. Ducts 29 and 34 are in hydraulic communication through bypass 35 and across one-way check valve 36 which permits flow from duct 29 into duct 34 but prevents reverse flow.

Axially aligned with duct 28 is tapered pin 38 integrally mounted on the chamber 15 side of piston 12. it will be seen that as piston 12 nears the end of its downward stroke approaching end wall 25, pin 38 will enter duct 28. Due to the taper of pin 38, flow through duct 27 will progressively be snubbed or metered until land 39 engages duct 28 to completely restrict flow therethrough. FIG. 4 discloses an alternate embodiment of the progressively restrictive orifice which will be described in greater detail hereafter.

- Transverse passage 26 is closed at both ends by plugs 40 and 7041 in threaded engagement in cylinder head 25. The restricting valve, generally designated by numeral 44, is slidably positioned in passage 26 and includes valve spool 42 which in a normal nonrestrictive position has its right end subject to pressure existing in duct 34 and its left end subject to pressure downstream of restriction 30. The positioning of spool 42 is controlled by biasing spool 46 acting through pin 43. Biasing spool 46 abuts the left end of pin 43 and is provided with a recessed seat 47 at its opposite end which receives spring 48 acting against plug 40 and spool 46. As will be explained in more detail hereinafter, the force of spring 48 alone is insufflcient to urge spool 46, pin 43, and valve spool 42, to their extreme rightward positions against the pressure force acting against the spool. However, the pressure exerted by fluid in duct 33 acting against seat 47 of spool 46 assists the force of spring 48, and only when this pressure drops below a certain predetermined value will the spool mechanism 44 be allowed to move to the left to restrict flow from the cylinder. Biasing spool 46, pin 43, and spool 42, may be affixed to each other, making spool 44 integral, or spool 46 may simply abut pin 43, in either case operation of valve 44 is essentially the same.

The left end of spool 42 is provided with a slotted axial opening at 45. Lateral openings extend into slot 45 and serve as metering orifices to stabilize operation as spool 42 moves to the left and begins to restrict flow through passage 30 into duct 29.

OPERATION FIGURE 1 When directional control valve 19 is moved to the right (straight through position), pressure fluid from pump 16 is admitted to cylinder chamber 14 through line 17 and passages 33 and 32, causing piston 12 to retract with its external work load.

Fluid pressure delivered by pump 16 through passage 33, along with the force exerted by spring 48, holds spool assembly 44 in the right nonrestricting position. As piston 12 moves inwardly, fluid is exhausted through passage 27, return line 18, to reservoir 20. Fluid discharge through orifice 30 in passage 27 will result in a pressure drop and a differential pressure between chamber 15 and duct 29. This same differential will also exist, since 34 is at chamber pressure, across spool 42. Although the right end of spool 42 is subject to the pressure existing in chamber 15 through communication therewith by passage 34, spool 42 is normally held against right hand plug 41 by spring 48 and the inlet pressure existing in chamber 33, and does not restrict flow through passage 27.

If the momentum of the external load causes piston 12 to accelerate, the fluid flow velocity through passage 27 will increase, increasing chamber pressure and the pressure differential across spool 42. If the piston travel velocity becomes excessive, that is the volume of chamber 14 is expanding more rapidly than the flow capacity of pump 16, a pressure loss occurs in chamber 14, duct 32, passage 33, and line 17. This pressure loss, since spring 48 is by itself insufficient to rightwardly bias spool 42 against the pressure force applied to its right end allows biasing spool 46, pin 43, and valve spool 42 to move to the left. Restriction of flow through orifice 30 will immediately begin as the left end of valve 42 enters section 30 of the transverse bore 26.

As the discharge flow is restricted by spool 42, the pressure in duct 28, chamber 15, and duct 34 will increase, thus stopping leftward movement of valve 44 and resisting the inward movement of piston 12 and retarding its travel. As piston 12 is decelerated, the discharge volume of pump 16 again becomes adequate to meet the system requirements and pressure increases in chamber 14 and accordingly in passage 33. The increase in pressure in passage 33 acting against the left end of spool 46 at seat 47, along with the force exerted by spring 48, will return spool 46 to the right, which through pin 43 urges spool 42 to the position shown in FIG. 1, allowing unrestricted flow through discharge passage 27.

As the piston travel continues toward end 25, taper pin 38 will enter the upper end of passage 27 progressively reducing the size of the discharge passage opening. The reduction causes a pressure increase in chamber 15 which quickly decelerates the piston velocity. When land section 39 of the pin enters in passage 27, all flow through the passage is blocked.

It should be noted that the piston velocity and cushioning controls are independent of each other and need not be used conjointly. The operation of the velocity control does not depend upon progressively restrictive oriflcing near the end of the piston stroke.

To return the cylinder to an extended position, directional control valve 19 is placed in its right-hand position. The weight of theload or some mechanical force acts to extend rod 13, and piston 12 moves upward. Oil in chamber 14 is released to reservoir 21 through passages 32 and 33 and line l7. Pump oil is recirculated to the reservoir. To prevent cavitation in fluid-filled chamber 15, bypass line 22 with oneway check valve 23 allows supplemental flow into chamber I5 through passage 27. During initial movement of piston 12 away from head 25, flow into chamber 15 will be bypassed from passage 29 across check valve 36. Once passage 27 is not restricted by land 39 of taper pin 38, supplemental fluid will pass through passage 27 directly into chamber 15.

DESCRIPTION FIGURE 2 This FIG. is similar to FIG. I, but includes the piston velocity control in conjunction with a double acting cylinder. In the description of this and the subsequent FIGS., the same reference numerals indicate similar elements but are distinguished in different parts of the FIG. with an appended letter. In the design of cylinder shown in this FIG., both chambers 14a and 15a can be supplied with pressure fluid, whereas the cylinder shown in FIG. 1 is single acting and can be operated hydraulically in one direction only. The valving providing the piston velocity control in both the rod end 25b and the head end 25a of cylinder 11a, is the same as that shown and described with reference to FIG. 1. The upper end of passage 33a is in hydraulic communication with duct 29b of passage 27b through conduit 51. Cylinder chamber is in hydraulic communication with passage 33b through conduit 50. Passage 33b intersects transverse bore 26b but is closed at its inner end and does not communicate with cylinder chamber 14a.

Chamber 14a is also provided with metering pin 38b which is aligned to enter passage 27b to progressively restrict discharge flow to decelerate and cushion the piston smoothly at the end of its stroke. Because of the central axial piston rod 13a which extends through end 25b of the cylinder, both the bore 26b and cooperating valving spool assembly 44b in head 25b as well as the metering pin 38b and passages 33b, 27b, and 34b, must be radially displaced from a center position in the cylinder so as not to interfere with the piston rod.

OPERATION FIGURE 2 The operation of the differential pressure-controlled flowrestricting valve spools 44a and 44b is identical to that described with reference to the FIG. 1 embodiment. The spool mechanisms serve to limit the velocity of the piston in either directions of piston travel, when the flow requirements to the expanding cylinder chamber are not being met by the system as indicated by a drop in the pump supply pressure to the expanding chamber.

If control valve is actuated to the right (straight through position), fluid pressure is delivered to cylinder chamber 14a through line 17a, passage 33a, conduit 51 and passage 27b. Discharge of fluid from chamber 15a is through passage 27a in head end 25a and line 18a to reservoir 200. If the velocity of piston 12a becomes excessive and a loss of supply pressure occurs, it is also reflected in a pressure drop passage 330. This allows the pressure impressed against the right end of 42a to overcome spring 48a to move spool 42a to a flow-obstructing position in orifice passage 30a. The obstructing of discharge flow causes a buildup of pressure in chamber 150, decelerating the piston [20. Piston deceleration is reflected by a pressure increase in chamber 140 and accordingly passage 33a and against spool seat 47a which acts to reposition spool 42 to its right-hand, nonrestricting position.

Similarly to extend the piston rod 13a, valve 19a is moved to the left (crisscross position), pressurizing chamber 15a through line 18a and passage 27a. Initially, if the rod is fully retracted, pressure fluid will be bypassed through duct 35:: and check valve 36a until metering pin 38a moves out of passage 27a and fluid is allowed to flow therethrough. Pump discharge pressure in chamber 27a is sensed in passage 33b through conduit 50. Discharge fluid from chamber 14a flows through passage 27b and by orifice 30b, through conduit 51, passage 33a and line 17a to reservoir a. If the velocity of piston 12a becomes excessive and a pressure loss occurs in chamber 150, spool 46b will be allowed to move to the left as a result of the corresponding pressure drop in passage 33b.

The movement of spool 46b then allows the pressure differential that is imposed across spool 42b then allows the pressure differential that is imposed across spool 42b to act to immediately move spool 42b to obstruct flow at orifice 30b, resulting in a pressure increase in chamber 14a to oppose the piston travel. When pressure in chamber 15a is restored, spool 46b is forced to the right, also forcing pin 43b and metering plug 42b to the right, again allowing unrestricted discharge flow through 30b.

As piston 12a travels toward end wall b, metering pin 38b also continues its travel and begins to enter chamber 271). As the piston movement continues, pin 38b acts to progressively restrict flow out of chamber 14a, cushioning the deceleration of the piston.

FIGURE 3 FIG. 3 shows the piston velocity control in a tandem cylinder system. In addition to the velocity control spool assembly, each cylinder is also provided with another valve spool which assists the variably orificed discharge in cushioning the piston at the end of its stroke as well as providing a flow-diverting or shunting function when a substantial pressure exists in the discharge chamber of the cylinder. Identical elements of the two cylinders of this FIG. and of other F 168., are identified by the same number, but are distinguished by the appended small letters 0 and d.

In FIG. 3, two identical cylinders 11c and 11d are connected to operate in tandem and receive fluid pressures from pump 160 through directional control valve 190. In tandem the cylinders operate synchronously so that one of the cylinders is retracting at the same rate the other is extending. Tandem arrangement is particularly suited for laterally swinging a boom of a backhoe or the like about a pivot point. Proper control of the swing velocity of backhoes is extremely important to prevent high-inertia loads from seriously damaging equipment.

In the present system, in addition to valve spools 44c and 44d, which as previously described in detail function to control piston velocity, cylinders 11c and 11d are provided with a second, separate valve spool assembly 75c and 75d respectively. Looking at right-hand cylinder llc andF 1G. 5 which shows the spool in greater detail, with this description applying equally well to cylinder lld, spool bore 76 transversely intersects the lower extension of passages 33c, 29c and 340. The left end of the bore is closed by threaded plug66. The right end is closed by plug 65, also threaded into the cylinder. Plug 65 extends into bore 76 to a point midway between passages 34c and 29c, and is provided with a cross bore 71 in through communication with passage 340.

A slidable pin 67 is centrally aligned within plug 65 and in a normal position extends from within cross bore 71 to the left end of the plug. Spool element 70, in a nonactuated position as shown, is held in abutment, partially by spring 55 of predetermined size, against the left end 2c, plug 65. The left end of spool 70 is bored at 79 to seat the spring 55 which extends between the seat and plug 66. Annular groove 78 axially defined by lands 73 and 74, is provided in the body of spool 70. Seat 79 of spool 70 is in communication with the pressure existing in passage 29c through hole 80 opening into groove 78. In a normal unobstructing position, the annular groove 78 permits unobstructed flow through passage 29c, and spool 70 as constructed does not block flow through passage 330. When spool 70 is leftwardly actuated so that spool land 73 moves at least into passage 33c, passage 330 is placed in communication through annular groove 78 with passage 290, while flow is still permitted unobstructed through passage 33c.

OPERATION FIGURE 3 As mentioned above, cylinders 11c and 11d are arranged in a system to operate synchronously in tandem. When the manual control valve 190 is actuated to the right (straight through position), fluid from pump 16c is introduced into chamber 15d of cylinder 11d through line 63 and passage 27d to move piston 12d upward in the cylinder and extend piston 12d. Pressure fluid also flows out of chamber 1511, through passage 34d and line 61 into passage 33c, and through line 32c into chamber 14c of cylinder 11c, imparting an inward travel to piston 12c. Discharge fluid from chamber 14d flows through line 32d, passage 33d, line 62, and passage 340 to chamber 15c. The discharge from chamber 15c flows to reservoir 200 through passage 27c and line 64.

If a condition arises under which there is a loss pressure in chamber 14c and pistons 12c and 12d are speeding, valve spool 440 in retracting cylinder 11c will act to orifice flow at 30c, as heretofore described, creating a back pressure in chamber 15c, thereby decelerating piston 126. The back pressure will also be sensed through the circuit in chamber 14d of cylinder 11d to decelerate piston 12d.

Valve spool assembly 750 in the'retracting cylinder functions to cushion the piston stop at the completion of retraction, as well as assists to decelerate piston velocity during the stroke. When, for example, during operation the inertia of the load accelerates piston to a velocity which exceeds the capacity of pump 16c, a pressure drop occurs in chamber and, accordingly, passage 330. The right end of pin 67 is sub- I ject to the high pressure in chamber 15c and the pressure differential, acting through pin 67, causes leftward actuation of spool 70 until land 73 moves into passage 33c and land 74 is in passage 29:, placing passage 33c and 29c in hydraulic communication through groove 78. Discharge flow from chamber through passage 29c and pump flow through 33c will follow the path of least flow resistance. If a reduced or partial vacuum exists in chamber 140, discharge flow from chamber 150 will be diverted through groove 78 into passage 33c and conduit 32c into chamber 14c, as well as to chamber 15d through line 61. When pressure builds in chamber 14c and passage 33c, fluid from passage 33c will pass through groove 78 to line 64 to tank, thereby relieving pressure in chamber 14c to reduce the driving force and the velocity of piston 12c. This also reduces pressure in chamber 15d to reduce the speed of piston 12d as well as piston 12c.

Once piston speed beings slowing, the pressure force exerted against pin 67 diminishes enough to be overcome by the force of spring 55, causing spool 70 to move to the right isolating passages 33c and 29c. The increase in pressure in passage 33c moves valve 44c to the right to allow efficient, unobstructed discharge flow. In this manner, piston velocity is limited to a predetermined maximum. Thus, during the velocitycontrol phase of the control operation, valve spool assembly 75c assists by preventing cavitation and relieving pressure from the expanding interconnected chambers 14c and 15d. Valve 75c is not conditional on supply pressure and responds only to a predetermined increase in pressure in the cylinder discharge chamber to be moved to a shunting position.

As the piston 12c approaches the end of its stroke, metering pin 380 will enter the upper end of 290 and begin to orifice flow of discharge fluid from chamber 150. A pressure rise occurs in chambers 15c and 34c which causes pin 67 to actuate spool 70 to the left placing passages 33c and 290 in communication through groove 78. Pressure fluid flow from pump 16c to chamber 14c is diverted through groove 78 to passageway 29c and through return line 64 to reservoir 20. Drop of pressure in chamber 14c allows the back pressure in chamber 15c to better decelerate and cushion piston movement and permits valve 44c to move into a flow-restricting position to further assist in cushioning.

Piston 12c comes to a stop fully retracted and the system becomes static with the pressure in passages 27c and 340, and chamber 15 going to zero. This allows spool 70 to return to the right in a nondiverting position.

By moving control valve 19c to the left (crisscross position), passage 27c becomes the inlet to chamber 15c and pistons 12c and 12d reverse their direction of travel. Since piston 12c is fully retracted against head 25c, inlet flow will be introduced through passage 29c, across bypassage 35c and the check valve and into chamber 15c. Inlet flow to cylinder 11d is from passage 34c, line 62, passage 33d, duct 32d to chamber 14d.

Discharge from chamber 140 will flow through 32c, 33c, 61 and 34d into chamber 15d of cylinder 11d. Discharge flow from 15d will be through passage 27d of cylinder 11d to line 63 and to reservoir c. Valve 75d in retracing cylinder 11d, will now function in the manner described with reference to 750 to divert flow in the cushioning and acceleration control phases. Valve 44d will operate in the circuit as described with reference to cylinder 11c, performing the piston velocity control by selectively orificing discharge flow from cylinder chamber 15c.

FIGURE 4 FIG. 4 depicts an alternate form of the progressive metering device which acts to restrict flow out of the cylinder at the end of the stroke to provide a cushioned cylinder stop. With the present embodiment, the necessity for the metering pin38, bypass 35 and one-way check 36 is eliminated.

In this embodiment, instead of the tapered metering pin, the piston and piston rod are provided with an axial bore 101 in alignment with upper duct 28 of inlet-discharge passage 27 in cylinder end wall 25. Slidably located within bore 101 is cylin- 40 drical plunger 85 having central axial flow passage 96 with orificed inlet 88 near the inner end. A compression spring 89 extending between the end of plunger 85 and the bottom of the axial bore will extend the plunger as the piston extends. Spring guide 93 extends from the bottom of bore 101 within the spring. Guide 93 is hollow and open-ended and provided with openings in the sidewall so that fluid may flow through passage 96 with a minimum of obstruction. Skirt 86 at extreme inner end of plunger 85 serves to guide the relative travel of the plunger within the bore and also contacts a mating stop 98 on the bore sidewallwhich limits the extension of the plunger. An orifice 92 in the recessed face 91 of the plunger affords communication between passage 96 and the inlet-outlet passage 28 of the cylinder.

The piston 95 contacts stop 94 to limit the inward travel of the piston so that plunger 85 is not fully retracted when the piston is fully retracted. A tapered notch 99 extends axially along the plunger wall and cooperates with bore 101 at 100 to provide a progressive orifice for discharge flow.

OPERATION FIGURE 4 The operation of the plunger-type flow-restricting member is as follows: With the piston 95 fully retracted, fluid is admitted to inlet passage 28. The fluid pressure acting against the face 91 of the plunger 85 forces the plunger inward compressing spring 89. This admits fluid to the head end of the cylinder chamber actuating the piston. As the piston extends, spring 89 causes plunger 85 to extend until skirt 86 engages mating stop 98. When the piston travel is reversed and the piston approaches end 25 of the cylinder, the end of plunger 85 contacts the cylinder head end 25 and shuts off direct flow from the cylinder chamber to discharge 28. The discharge flow must now pass along taper groove 99, through orifices 88, into passage 96 and through orifice 92 to discharge passage 28. As the piston moves inward, plunger further retracts to progressively orifice discharge flow as the volume of fluid flowing into passage 28 is limited by the opening defined by groove 99 and cooperating wall 100. From this description it will be seen that the extension of the piston from a fully retracted position can be accomplished with the use of the present plunger-type progressive orifice, eliminating the need for a separate bypassage. This mechanism could be substituted for the tapered metering pin or similar snubbing device for cushioning the piston stop.

Although I have described the novel velocity and cushioning control devices herein with reference primarily to linear actuators, it will be obvious that the invention herein can be modified and is equally adaptable for use with rotary actuators. To the extent that such modifications and changes do not depart from the spirit of the invention, they are intended to be included in the scope thereof, which is not limited to the embodiments specifically illustrated in the drawings, but rather only by a just and fair interpretation of the claims.

Having clearly described the invention and thereby enabling those skilled in the art to construct and use its principles, I claim:

1. in a hydraulic actuator including a cylinder defining a working chamber and having an end wall, a piston and rod reciprocable in said chamber and dividing it into a first variable volume chamber in the rod end of the cylinder and a second variable volume chamber adjacent the end wall, a first passage in said end wall connected to said first chamber which serves as an inlet for hydraulic pressure fluid when said first chamber is expanding in volume, a second passage in said end wall connected to said second chamber and which serves as a discharge passage when said second chamber is contracting in volume, a piston velocity control which comprises:

a transverse passage in the cylinder end wall communicating with said first and second passages and intersecting said second passage to define a flow restriction in the path of flow through said second passage;

a duct communicating said second chamber with said transverse passage;

valve means slidable in said transverse passage having one end exposed to the reduced pressure in the discharge passage at the discharge side of the flow restriction and the other end subject to chamber pressure existing in said duct; said valve means having an open position which allows unobstructed flow through said second passage and a closed position which restricts flow through said second passage;

valve-controlling means including reciprocable plunger means in said transverse passage which bias said valve means in said normally open position, said valve-controlling means being held in a biasing position by a predetermined inlet pressure in said first passage whereby a loss in inlet pressure to a predetermined level attendant excessive piston velocity allows the valve means to override said bias to move to a closed position and restrict flow through said discharge chamber while permitting unrestricted flow through said discharge chamber while permitting unrestricted flow through said first passage; and

said valve-controlling means including a spring exerting a force to assist in holding said valve spool in a normally open unobstructing flow position.

2. The apparatus of claim 1 provided with means movable by and with the piston which cooperate with said second passage to additionally and progressively further restrict the flow of fluid from the cylinder outward through said second passage to decelerate and cushion the stop of said piston as the piston approaches said end wall.

3. The apparatus described in claim 1 further provided with a bypassage in the cylinder end wall communicating at one end with said second passage and at the other with said second chamber and having a check valve associated therewith to permit flow only from said second passage into the second chamber.

4. The apparatus of claim 1 wherein said cylinder is further provided with a second transverse passage communicating with said first and second passages,

a cannelured valve spool slidably disposed in said second transverse passage, said spool in a first position blocking flow between said first and second passages and in a second position establishing communication between said first and second passages, said spool being normally biased to said first position and being pressure responsive to a predetermined pressure in said second chamber to overcome said bias to move to said second flow position and permitting flow through said first passage in both positions.

5. The apparatus of claim I wherein said valve means is provided with metering orifices which permit a predetermined discharge flow through said second passage when said valve means is in a closed position.

6. A hydraulic system comprising: a first and second hydraulic cylinder each having an end wall; a piston and rod reciprocable in each cylinder dividing each into a first variable volume chamber in the cylinder rod end and a second variable volume chamber adjacent said end wall; each cylinder including a first inlet'discharge passage in direct communication with said first cylinder chamber, a second inlet-discharge passage in communication with said second chamber, and a third recirculation passage in said end wall in communication with said second chamber; a source of fluid pressure having a low-pressure supply reservoir connected to a control valve; conduit means interconnecting said first and third passages of said first cylinder with the third and first passages of said second cylinder respectively; said second inlet-discharge passages of said first and second cylinders being selectively connectable to said pressure source and reservoir through said control valve for tandem operation whereby one piston rod is extending while the other is retracting; a transverse passage in each cylinder end wall communicating with said first, second, and third passages; valve means slidably positioned in said transverse passages, said valve means having a first nonobstructing position and second position effective to restrict discharge flow through said second inlet-discharge passage of the retracting cylinder, said valve means being normally biased to said first position by pressure fluid in said first passage in said retracting cylinder, and being pressure responsive whereby a predetermined reduction in pressure in the retracting cylinder chamber allows said valve means to overcome the bias to move into said second position to restrict discharge flow thereby controlling the velocity of the pistons. 7. A hydraulic system comprising:

a first and second hydraulic cylinder each having an end wall;

a piston and rod reciprocable in each cylinder dividing each into a first variable volume chamber in the rod end and a second variable volume chamber adjacent said end wall;

each cylinder including a first inlet discharge passage in direct communication with said first cylinder chamber, a second inlet-discharge passage in communication with said second chamber, and a third recirculation passage in said end wall in communication with said second chamber;

means interconnecting said first, second, and third passages of said first and second cylinder for tandem operation whereby one piston rod is extending while the other is retracting, said means interconnecting the expanding cylinder chambers to a common supply of pressure fluid and the contracting chamber to a common discharge;

a transverse passage in the cylinder end walls communicating with said first, second, and third assages; pressure responsive valve means slida le in said transverse passages having a first nonobstructing position and a second position effective to restrict discharge flow through said second passage, said valve means operative in the retracting cylinder and being normally biased to said first position by pressure fluid in said first passage in the retracting cylinder and being pressure responsive whereby a predetermined reduction in pressure in said retracting cylinder first passage allows said valve means to overcome the bias to move into said second position.

8. The apparatus of claim 7 provided with means movable by and with the piston of said first and second cylinder which cooperate with said second passages in said cylinders as said pistons retract to additionally and progressively further restrict the flow of fluid from the cylinders outward through said second passages to decelerate and cushion the stop of said pistons.

9. The apparatus of claim 7 wherein each of said cylinders is further provided with a bypassage in the cylinder end wall communicating at one end with said second passage and having a check valve associated therewith to permit flow only from said second passage into the cylinder.

10. The apparatus of claim 7 wherein each of said cylinders is further provided with a second transverse passage commu nicating with said first and second passages,

a cannelured valve spool slidable disposed in said second transverse passage, said spool in a first position blocking flow between said first and second passages and in a second position establishing communication between said first and second passages, said spool being normally biased to said first position and being pressure responsive to a predetermined second chamber pressure to overcome the bias to move to said second flow position and permitting flow through said first passage in both positions. 

1. In a hydraulic actuator including a cylinder defining a working chamber and having an end wall, a piston and rod reciprocable in said chamber and dividing it into a first variable volume chamber in the rod end of the cylinder and a second variable volume chamber adjacent the end wall, a first passage in said end wall connected to said first chamber which serves as an inlet for hydraulic pressure fluid when said first chamber is expanding in volume, a second passage in said end wall connected to said second chamber and which serves as a discharge passage when said second chamber is contracting in volume, a piston velocity control which comprises: a transverse passage in the cylinder end wall communicating with said first and second passages and intersecting said second passage to define a flow restriction in the path of flow through said second passage; a duct communicating said second chamber with said transverse passage; valve means slidable in said transverse passage having one end exposed to the reduced pressure in the discharge passage at the discharge side of the flow restriction and the other end subject to chamber pressure existing in said duct; said valve means having an open position which allows unobstructed flow through said second passage and a closed position which restricts flow through said second passage; valve-controlling means including reciprocable plunger means in said transverse passage which bias said valve means in said normally open position, said valve-controlling means being held in a biasing position by a predetermined inlet pressure in said first passage whereby a loss in inlet pressure to a predetermined level attendant excessive piston velocity allows the valve means to override said bias to move to a closed position and restrict flow through said discharge chamber while permitting unrestricted flow through said discharge chamber while permitting unrestricted flow through said first passage; and said valve-controlling means including a spring exerting a force to assist in holding said valve spool in a normally open unobstructing flow position.
 2. The apparatus of claim 1 provided with means movable by and with the piston which cooperate with said second passage to additionally and progressively further restrict the flow of fluid from the cylinder outward through said second passage to decelerate and cushion the stop of said piston as the piston approaches said end wall.
 3. The apparatus described in claim 1 further provided with a bypassage in the cylinder end wall communicating at one end with said second passage and at the other with said second chamber and having a check valve associated therewith to permit flow only from said second passage into the second chamber.
 4. The apparatus of claim 1 wherein said cylinder is further provided with a second transverse passage communicating with said first and second passages, a cannelured valve spool slidably disposed in said second transverse passage, said spool in a first position blocking flow between said first and second passages aNd in a second position establishing communication between said first and second passages, said spool being normally biased to said first position and being pressure responsive to a predetermined pressure in said second chamber to overcome said bias to move to said second flow position and permitting flow through said first passage in both positions.
 5. The apparatus of claim 1 wherein said valve means is provided with metering orifices which permit a predetermined discharge flow through said second passage when said valve means is in a closed position.
 6. A hydraulic system comprising: a first and second hydraulic cylinder each having an end wall; a piston and rod reciprocable in each cylinder dividing each into a first variable volume chamber in the cylinder rod end and a second variable volume chamber adjacent said end wall; each cylinder including a first inlet-discharge passage in direct communication with said first cylinder chamber, a second inlet-discharge passage in communication with said second chamber, and a third recirculation passage in said end wall in communication with said second chamber; a source of fluid pressure having a low-pressure supply reservoir connected to a control valve; conduit means interconnecting said first and third passages of said first cylinder with the third and first passages of said second cylinder respectively; said second inlet-discharge passages of said first and second cylinders being selectively connectable to said pressure source and reservoir through said control valve for tandem operation whereby one piston rod is extending while the other is retracting; a transverse passage in each cylinder end wall communicating with said first, second, and third passages; valve means slidably positioned in said transverse passages, said valve means having a first nonobstructing position and second position effective to restrict discharge flow through said second inlet-discharge passage of the retracting cylinder, said valve means being normally biased to said first position by pressure fluid in said first passage in said retracting cylinder, and being pressure responsive whereby a predetermined reduction in pressure in the retracting cylinder chamber allows said valve means to overcome the bias to move into said second position to restrict discharge flow thereby controlling the velocity of the pistons.
 7. A hydraulic system comprising: a first and second hydraulic cylinder each having an end wall; a piston and rod reciprocable in each cylinder dividing each into a first variable volume chamber in the rod end and a second variable volume chamber adjacent said end wall; each cylinder including a first inlet discharge passage in direct communication with said first cylinder chamber, a second inlet-discharge passage in communication with said second chamber, and a third recirculation passage in said end wall in communication with said second chamber; means interconnecting said first, second, and third passages of said first and second cylinder for tandem operation whereby one piston rod is extending while the other is retracting, said means interconnecting the expanding cylinder chambers to a common supply of pressure fluid and the contracting chamber to a common discharge; a transverse passage in the cylinder end walls communicating with said first, second, and third passages; pressure responsive valve means slidable in said transverse passages having a first nonobstructing position and a second position effective to restrict discharge flow through said second passage, said valve means operative in the retracting cylinder and being normally biased to said first position by pressure fluid in said first passage in the retracting cylinder and being pressure responsive whereby a predetermined reduction in pressure in said retracting cylinder first passage allows said valve means to overcome the bias to move into said second position.
 8. The apparatus of claim 7 provided witH means movable by and with the piston of said first and second cylinder which cooperate with said second passages in said cylinders as said pistons retract to additionally and progressively further restrict the flow of fluid from the cylinders outward through said second passages to decelerate and cushion the stop of said pistons.
 9. The apparatus of claim 7 wherein each of said cylinders is further provided with a bypassage in the cylinder end wall communicating at one end with said second passage and having a check valve associated therewith to permit flow only from said second passage into the cylinder.
 10. The apparatus of claim 7 wherein each of said cylinders is further provided with a second transverse passage communicating with said first and second passages, a cannelured valve spool slidable disposed in said second transverse passage, said spool in a first position blocking flow between said first and second passages and in a second position establishing communication between said first and second passages, said spool being normally biased to said first position and being pressure responsive to a predetermined second chamber pressure to overcome the bias to move to said second flow position and permitting flow through said first passage in both positions. 